Getter for controlling crystal growth



Patented May 3,1927- "1 momma STATES WILLIAM CHARLES sraoassna, or iaLoomrmLn, new masamnssmnoa 'ro WEST-f menousa LAMP cournrz, a coaronarrou or rnuusxavaxra.

oz'r'rnn roa con rrmmime caxs'rar. eaow'rn.

Io Drawing. 1

This invention relates to getters and more particularly to such'conta'iriing phosphorus and a refractory oxide such as thorla.

An object of'my invention is the pro- 5 vision of a getter suitable for use on thoriated wire or filamentary, material without initial reduction of the thoria content in said wire.

Another object j of my invention is the introduction of an oxide, such'as thoria, into getters containing phosphorus to prevent the reduction of thoria in flthor'iated fila-' mentary material, when such" 'etters are activated after application to sue material.-

A further object" of myginvention is to protect the thoria in filamentary material from the initial reducing effect of ho sphorus in getters, by incorporating t oria m" such getter before application to the filamentary material.

,A-still further object of my invention is:

i a getter adapted to a e a pliedto filaments for incandescent electric amps and containing a refractorv oxide'such as silica, alumma, or beryllium oxide. According to said application, a preferred substance was silica and a satisfactory etter was prepared by mixing together the ollowing active in-' gradients with approximately the following percentages-by weightz-silicon oxide 40%,-

phosphorus' 10% and cryolite Although such getter has been found very crease in the life of .the lamp was effected. -Further research has resulted in the development of a getter which not only accomplishes the results obtained by the silica getter aforementioned, but causes 'an increase inthe life of, afilament to which it effective in greatly increasing the bump-test strength of a filament afterflashing, no in ap licat on filed master 6, m2. Serial x'ojsoazsi.

has been applied. -This result is accom plished without a decrease in initial efficiency of the lamp.

.Thoria-containing getter prepared according-tomy invention has the property of: reducing the average temperature of a filament when initially lighted. Such agetter is therefore effective in .tontrollmg the rate of crystal growth of thoriated metallic material, such as tungsten, while suchm ate-v rial in filamentary form is beingflashed. It

has been I shown by G. i J. Smithells, Trans actions Faraday Societ June 22; 1921,-t hat the deformation of a lament which occurs 6 I during life is a function; of the crystal r growth.- It is known that thethoria content of tun ten filamentary material retards. .the rate o the crystal rowth andthereby reduces deformation oft efilament. .Thoria,'- aswell as other refractory oxides,xcan be,

reduced, to some extent, .byfphosphorus I and other reducing agents at "hightempejra ture.

The greater pro ortion' of vvacuum t pe lamps are only fias led before being pac ed,

for shipment.- Such flashing is-necessary for lnspectlon purposes and. in order to If alamp were initially lighted on designed voltage with-.-

out ballast resistance before being flashed,

it would very" likely burn out immediately.

' With an ordinary phosphorus-cryolite getter, the flashing operation results in greatly reduced filament strength on acount of temperature gradients and excessive heating of the filament, especially the lead-in Strands. With the use of a refractory oxide, such as thoria, temperature gradients at flashing are almost entirely eliminated and the filament. does not. become overheated.

.This results in retardationof crystal growth,

which leaves the filament stronger'and less liable to be broken during shipment. j i

invention obviatesa possible initial reduction of the thoria content in a. filament,

to which a phosphorus containing getter,-

has been applied, by incorporating thoriav orits equivalent in such getter. When the getter is activated, the phosphorus will act upon the thoria' incorporated therewith,

which will protect the thoria contentin the filament from possible reduction by the ie: phosphorus in the getter. Thoria being highly refractorywillbe retained in part, at least, on the filament and will serveto in-' crease the strength thereof.

My invention is especially adapted for a phosphorus containing getter. 'Ithas been customary to use a getter, called 3113, containing 100 parts, y weight, of cryolite and 13 parts, by Weight, of phosphorus and I have found-that suchagetter is very favorably modified by replacmg from 20 to 25 parts of the cryolite content by the same amount, by weight, of thoria. It has been found from the results of a. large number of tests, thatlamps made with thoria ,get-

tors equal in bump-test strength after the flashing treatment,thelampsmade with a silica getter and at the same time an improvement in life is effected, as compared 'with the life of such a lamp when using the ordinary phosphorus-cryolite getter.

In regardto bump-teststrength, the 1esults show that the increase varies up to over 10.0%,with 50% representing about the average increase. From" life testing lamps using a thoria getter indicated that as an avera e, a 15% increase in life may be exte with .the use of such getters.

.The. advantages of using thoria as a comnent of a getter material areas follows.

hria,'beinginert with respect to tungsten,

'will noticause any deleterious reaction therewith... thoria remaining on the filament afar fias ing, will not reduce the initial efficiency of the lamp, in fact, incandescent 'thoria having a higher selective light emission-than tungstem-should cause im rovement in luminosity. Further, if as is be ieved b a few authorities, part of the thoria of a tlloriated' filament is reduced by phosphorus I introduced with the getter, when the getter is activated-theuse of-thoria getters should materially ecrease such reaction by providipgadditional thoria for the phosphorus to react with, instead of with the th'oria'contentofthefilament'."

.To""explain'- the increase in filament strength effected by; the use ofthoria getthesame reasons can be iven as those use chief reasons for the increase in filament strength when refractory substances are used, is that of reducing temperature gradients to a minimum, particularly at the flashing o eration.

' j pesirab e results have been obtained by ff using thoria which was heated to a temperature of 2000 C. before being incorporated with the other materials of the getter. The

heating may be done in a carbon resistance furnace using a carboru'ndum vessel as a container. Results in some early tests, where the clean-u s after. flashing were not satis factory, in icated that the thoria contained traces of occluded gases. Heating of the filament.

to explain that action with the use of silica getters'. It is thought that one of the done, satisfactoryresultswere obtained.

As a substitute'for thoria, 'elsbachmixture'has been tried, that is, thoria containing an admixture of 1% of ceria. Althou h it would appear thatsuch a mixture wou d effect the same result as thoria, it has not proven -to be entirely satisfactory, as the ceria appears to interact with the tungsten It will therefore be apparent that it is desirable to use very pure thoria, which should bet-horoughly incorporated with the other materials of the getter, for example, red phosphorus and cryolite. A preferred formula for a getter according to'my invention is approximately 20 to 25- parts, by weight, of thoria, 13 parts,.by wel ht, of phosphorus andfrom 80 to 7 parts, y Weight, of cryolite, althoughthe proportionsmay be varied. For exam le, satisfactory results have been obtained w en using up to 50 parts of thoria, with as little as 50 arts of cryolite and about 13 parts of phosp orus. A homogeneous mixture may be made of these substances and a thin coatinglthereof applied in any desired manner to t e filamentary ma terial; The coating may be dried and thereafter the coated filament severed into appropriate lengths'and mounted in an ineandescent electric lamp envelope in the usual method.

"The following table shows the life test results of lamps made with the usual phosphorus-cryolite or 31-13 getter, as compared to those made with such a getter in which part of the cryolite has been replaced by'tho ria. In thefirst-test only, the initial lumens v 1s expressed as candle power.

Lifetestresulte. Life mu Test Gemip Pet initial mean watts. mmwmw- Initial cont mam, y

" lumens. lumens dency dency maint. hours. hourl.

. 1.... 4o 20g.Th0;,80g. 4220?, am 1071 ms cry. 13 g. P. 1..-. 40 31 p, (10 9 cry., 0.1 or am ma 13st 2.... 4o g. 'rnoi, 15 g. 404 87.0 1099 1170 cry. 13 g. P. ,2-.-.. .40 503. 151101.503. 406 an 1225 1101 cry., 13 g. P. 2.... 4o -13 a 86.0 052 1023 2sa.'rho,,1sg 632 78.2 2080 ms cry.,13g 3.... to 31-13. m 80.1 1564 1623 4o 2ag.'rho,,75g. 400 86.4 1845 2002 cry.,13g. P. 4.... 4o wg.'rno,,aog. m an 1420 i365 cry. 131.2. 3 4...- 40 253.1110, 15 g. as em 1279 1430 cm, 13 g. P. 4...- 40 31-13. see am 754 991 4o 25g.'1h0|,75g an ass 10:54 1388 cry. 13 g. 5---- 4o 50g. '12105505 40o 88.0 1078 ,1223

cry. 13 g. -s-.... 40 so xrho -w 401 2.4.4- .1554 1510 cry.,-13 g. I 5-... 4o a1-1a ace 91.7 aoo 1290 Although havedescribed what is now' considered'the preferred embodiment of my invention it is to be understoodtha-t modifications maybe made therein withinthe spirit and scope of the appended jclaims.

. of cryolite.

What is claimed is: 1. A getter for application to a thoriated itungsten 'filamentfor an incandescent elec tric lamp comprls ng thoria for increasing the life and bump-test Strength of said filament. I I

2.- A getter for application to a thoriated tungstenfilament of an incandescent electric lamp comprising thoria "and phosphorus, the thoria. serving-to prevent'initial reduction of the thoria in the filament by the phos phorus duringrflashing, whereby the crystal growth restrainin'gefi'ect of the filamentcontained thoria is maintained. 1 4 a 3. A getter for a thoriated tungsten filament prepared accordingto approximately the following proportions: 20 to 25 parts by weight of thoria, about 13 parts by weight of phosphorus and 80 to 75 parts by weight 4. Inan incandescent electric lamp, a

getter comprising thoria and phosphorus, whereby excessive crystal growth in the filament is prevented.

I 6. In an incandescent electric lamp, 8.

thoriated tungsten filament having applied .thereto, a getterprepared according-to 'approximately the following proportions: 20 to 25 parts by weightof thoria, about 13, parts by weight of phosphorus and 80 to 75 parts by weight of cryolite, the thoria serving to prevent excessive, crystal growth in the filament.

In testimony whereof, I have hereuntosubmy name this 5th day of December,

scribed WILLIAM CHARLES SPROESSER. 

